Set in Karachi, and focused on the last three decades of Pakistani society and politics, Kamila Shamsie's richly woven fourth novel explores the relationship of a young and somewhat listless elite to a previous age of grander spirit and vision. Aasmaani is assailed by memories of the 1970s and 80s, when the nation could be made to buck and rear at the sound of her mother's political speeches or the biting allegories of the Poet, her mother's lover. Under the administrations of Zulfikar Ali Bhutto and Zia ul-Haq, the unrepentant couple went through police violence, imprisonment and exile, then the Poet was (if received wisdom is to be believed) violently murdered - and yet poetry, politics and love were grand, excessive and indispensable. Now, in times of less confrontation and more TV channels, nothing is so significant or deeply felt.

Aasmaani is expending her own intellectual and poetic gifts writing questions for a TV quiz show. "Politics" is exported, and reduced to a half-hearted consumer decision ("You really planning to boycott American goods when they attack Iraq?" - "Hanh, well, we have to feel like we're doing something, right?") and the Poet's erstwhile protege has become fat and complacent, producing "verses to fit the occasion for anyone willing to pay the price, regardless of their political affiliation". Lesser times, all in all; and Aasmaani's torment at having been rudely cut off from both her mother and her intellectual and literary mentor is thus also the anguish of no longer knowing how to be - the bewilderment of poverty after a rich tradition is exhausted.

Shamsie's exploration of this theme has moments of great power. The delight in words and all their shades of meaning, characteristic of all her writing, is here used as the linchpin of the plot, as dictionaries, crosswords, fairy tales and poems become keys to the coded messages whose authorship and purpose she is trying to understand. Aasmaani's lifelong familiarity with intrigue has also made her paranoid: she looks at everything with a hyper-aware suspicion - and this mixture of poetry and paranoia results in a scintillating and ever-expanding semantic universe, as she repeatedly re-examines the same set of facts and finds each time another poetic archetype or Sufi paradox that lends them an utterly new significance. The voice that guides us around this world darts with wit and lightness in a way that is unique and often lovely.

Given its grand themes of nation, politics and art, however, this book's philosophical arc is disappointingly constrained. When we finally leave her, she is making a documentary about her mother and the women's movement in Pakistan, still fixated on the grandeur of the past, and still anxious about the trivialising influence of foreign places and modern life. Ultimately, she remains inflexibly aristocratic, wistful for courtly thought and expression, and unable to see in the Pakistan of today, when the state's displeasure is focused on people very different from her, anything worthy of the name "history". It would have been gratifying to see this heroine's search open up newer and more challenging terrain, and thus end slightly further away from where we began.

Bloomsbury's bougainvillea-strewn edition of this book is exquisite, and there is a succulent pleasure to the narrative that draws you happily to its end. But as the pages run out, you begin to realise that there's not enough space left for the greater imaginative breakthrough you so hoped it would deliver.